Mousewheel scrolling a XAML panel containing a WebView2

[Marv51]

Describe the bug Scrolling with the mouse wheel when the pointer is over a WebView2 does not scroll the XAML panel of that WebView2. This worked in WebView(1) in UWP perfectly. Even when the WebView2 does not have scrollbars and the XAML panel (ListView) does have scrollbars, the mousewheel event seems to be triggered inside the WebView2 but never makes it to the XAML-Container.

(Setup for this is the same as my other WebView2 bug #4595)

Expected behavior If the Webview2 content is entirely shown on screen without scrollbars, the panel/container should scroll.

Screenshots This mostly shows the rendering issues I'm having (#4595), but maybe it helps?

https://user-images.githubusercontent.com/471338/111863665-422ad800-895d-11eb-8bb6-55e9e5cd2e36.mp4

Each frame is a ListView Item, title "Update *" is XAML TextBlock. Below which is a WebView2.

Version Info I'm on Project Reunion 0.5 Preview WinUI 3 Desktop. Windows 10 20H2 19042

Windows app type:	UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)	Yes
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional Context I guess I could work around this by creating the layout entirely in HTML and using only one WebView2, however this is a port from UWP and this worked perfectly before.

[StephenLPeters]

@anawishnoff fyi

[codendone]

We call this "scroll chaining", where any unusable amount of scrolling will chain up to parent containers. This is something we plan to support, but we don't currently have an ETA for this.

[Marv51]

"scroll chaining" is a very good way to describe it

[Marv51]

Keep alive (re #8638)